The art is replete with carrier tapes that are used to transport components (e.g. torsion springs, leaf springs, or electronic or electrical components such as resistors, flatpacks, capacitors, or integrated circuits) from a component manufacturer to a different manufacturer that assembles the components into new products, typically by having automated assembly equipment sequentially remove components from the carrier tape and subsequently use them in the assembly of the new products.
One type of carrier tape may comprise a polymeric strip that has been formed to have wall portions defining a series of identical pockets at predetermined uniformly spaced intervals along its length, which pockets are shaped to closely receive identical components that are adapted to be transported by the tape. For example, the pockets may comprise rectangular or generally "I" or "T" shapes in the plane of the strip, and may have flat or rounded bottoms to accommodate the shape of the components.
The tape strips normally have through openings uniformly spaced along each side to receive drive sprockets by which the strip can be driven and to provide indexing holes that can be used for accurately locating the pockets along the tape with respect to assembly equipment. The strips also typically have through apertures along middle portions of each of the pockets to provide a hole that can be used by the assembly equipment to determine whether a component is present within the pocket (e.g. by using an optical scanner).
Typically, the carrier tape is manufactured in a first manufacturing location, wound on a reel (e.g. the reel described in U.S. Pat. No. 4,893,764 the entire contents of which are herein expressly incorporated by reference) and transported to the supplier of the components that it is intended to transport. The component supplier unwinds the carrier tape from the reel, fills the pockets along the carrier tape with components, adheres a removable cover strip along the carrier tape over the component filled pockets, winds the component filled carrier tape with the attached cover strip onto a reel, and transports it to the user who feeds it from the reel into the assembly equipment which removes the components.
While such carrier tape can be formed by continuous injection molding, it is more commonly formed from an initially flat polymeric heated thermoplastic strip using a tool to form the pockets (e.g., male and female die sets, or a male or a female die over which the strip is vacuum formed).
Existing tape carriers encounter problems when they present their carried articles to automated assembly equipment. Maintaining a precise orientation of the carried article relative to the carrier tape is an important element in carrier tape performance. The tape carriers of the prior art tend to allow a misalignment or "shifting" of the orientation of the carried article within the pockets of the carrier tape. The misalignment may be described as a displacement in an X-Y plane or may be described as an angular displacement and may be caused by a variety of phenomenon such as vibration during shipping. Such a misalignment of the orientation of the article within the pocket may cause the automated assembly equipment (used to construct the new product) to position the article in an improper position on a printed circuit board in the new product.
In applications which require that a component be precisely located on a printed circuit board, the automated assembly equipment may include optical scanner mechanisms which are adapted to determine the orientation of the components with respect to the rest of the assembly equipment. Optical scanner mechanisms, however, are costly and require additional time during the assembly process.
One example of a component that may be carried by the carrier tape is a flatpack (i.e. gull wing, J-bend, and flying lead flatpacks) which includes a body and at least one connector pin or "lead" which affords connection of the component to an electrical circuit in the new product to be assembled by the assembly equipment. For example, a flatpack may comprise a rectangular shaped body having side walls defining corners, top and bottom walls and a plurality of leads which are spaced from the corners and which project generally normally away from the side walls and extend below the bottom wall.
Existing carrier tape encounters problems in protecting the carrier components. Generally, the components carried by the carrier tape are extremely sensitive and fragile and should be protected from mechanical damage from bending, fracturing, deflecting, breaking or other distortions in their original shape. Frictional wear is also a problem with the fragile leads. It is believed that leads may be damaged by even slight collisions with the structure of the tape, particularly when the electronic component is removed from the pocket. The three leads which extend the farthest below the bottom wall (i.e. the bottom three leads) define a lowest plane. In many applications, the remaining leads of the component should not be spaced more than 0.004 inches (0.1 mm) from this lowest plane. If a lead is spaced farther than 0.004 inches from this lowest plane, then the lead may not be connected to the circuit on the printed circuit board in the new product circuit on the printed circuit board in the new product resulting in a defective new product.
The art is replete with carrier tapes adapted to protect electrical components. One such tape is disclosed in PCT International Application, International Publication Number WO 90/04915 assigned to Reel Services Limited, GB. That carrier tape comprises a plurality of spaced walls defining identical pockets having projecting portions including rectilinearly extending separated portions and ridges which are aligned with the walls defining the pocket. The electrical component rests on the projecting portions until it is removed by a vacuum pick-up. Due to their close proximity relative to the leads of the electronic component, the projecting portions and ridges offer potential contact points with the leads, thereby increasing the potential for damage to the leads resulting from contact with the structure of the carrier tape. Additionally, when the component is lifted from the projecting portions, it sometimes tends to rotate relative to the bottom wall of the pocket. Such rotation of the electronic component is believed to expose the leads to damage such as bending due to contact with the projecting portions. Any rotation of the component with respect to the carrier tape may result in a misalignment of the component on the new workpiece, an undesirable result.
Electrostatic damage (ESD) is another problem associated with existing carrier tapes. Triboelectric charges may exist on the component prior to its being placed into the carrier tape, or may build on the component if its fit within the pocket is overly loose and thus permits the body of the component to rub against the tape structure and/or the affixed cover tape strip. At some time during the use of the carrier tape, particularly when the electrical component is removed from the tape pocket, such electrostatic charges may be discharged from the component to the carrier tape. Such a discharge may damage the component by, for example, damaging a dielectric layer within the component. This is the result of an excessively rapid discharge in which the resultant change in voltage divided by the change in time (.DELTA.V/.DELTA.t) across the dielectric layer exceeds the breakdown voltage of the dielectric material thereby causing its perforation. In some components, this damaging voltage differential may be as low as 50 volts or less. Carrier tapes for these types of components will thus have a surface resistance of greater than 10E04 and less than 10E12 (OHMS/square) and a concomitant volume resistivity of greater than 10E03 and less than 10E11 (OHM-CM).